


H2O

by MakikoIgami



Series: FFXV Promptis NSFW Week 2018 [5]
Category: Final Fantasy XV
Genre: Anal Sex, M/M, Mating Cycles/In Heat, NSFW Promptis Week 2018, Non-Human Genitalia, Non-Human Noctis, Other
Language: English
Status: Completed
Published: 2018-09-03
Updated: 2018-09-03
Packaged: 2019-07-06 09:37:32
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 7,317
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/15883422
Author URL: https://archiveofourown.org/users/MakikoIgami/pseuds/MakikoIgami
Summary: Prompto made a new friend a while ago. But his friend isn't human, his friend is the local siren.





	H2O

**Author's Note:**

> Day 05: Oral || Being pinned/fucked against the wall || **“Holy shit, dude. Did you just make that sound?”**
> 
> You: Hey, it's Mer-May! Why not make something with either of the boys as a mermaid?  
> Me, who has been in the Free! Fandom for years now: This is my time to shine!  
> Also me: I'll just write some short PWP.  
> Story: ends up being so long that I can submit it to the Promptis NSFW Week. XD  
> Well, it's late, I know. I started writing this on May 30th, after being a little frustrated with myself. I tried to distract myself with it and I hope you'll like it. It's... not the best, in fact it's really bad in some places, but I really like the end. I hope you'll like it, too. After all, this is longer than my submission for the previous days. ;D
> 
> Oh, the shape of the genitalia is like in [this art](https://yakipurin.tumblr.com/post/173586877696/i-am-not-so-sure-about-this-but-is-has-some-merman) by Banira. 
> 
> PS: I'll promise I'll answer all comments! But right now I'm a bit swamped with work and con preparations. ^^;

Prompto made his way down the beach, just like he had done every other night in the past few weeks. The small town where he lived had always told the legend of a siren living in the waters that protected them, but then one day, Prompto found out that these stories weren't just legends, but the truth. However, the siren wasn't big and scary, but looked more like a boy his age. Well, if boys his age had a fishtail, pointed ears, the sharpest teeth Prompto had ever seen in his whole life and eyes that glowed violet.

Of course, he had been scared. So scared that he had tripped over some ropes someone had left lying around and fell from the pier into the water. Who wouldn't have been if there was suddenly a creature with glowing eyes lurking in the dark body of water? So, even though Prompto had just so managed to throw his camera that he hoped was safe, he himself had ended up under water, limbs tangled up in those ropes that had come down with him and he would have surely died if not for the scary creature with the glowing eyes that hurried to his side and started to pull him out of the ropes. Unfortunately, Prompto hadn't known that at the moment, so he struggled until he lost consciousness.

The next thing he saw as he woke up were a pair of beautiful stormy grey-blue eyes looking down at him, and he found himself so mesmerized that he didn't even black out again when he had to face a very sharp, toothy grin.

"You're alive!" The creature said and leaned back to give Prompto some space to sit up. Prompto's blue eyes were wide as he kept staring at his savior in wide disbelief. 

"You... can talk!" Prompto squeaked, while he looked a little closer at the other male. He was covered with black scales that shimmered golden in the waning light from his pointy ears down to the tip of his fish tail. From the waist up, the siren looked more like a human than a monster and Prompto blinked owlishly at him. He was beautiful.

"Of course I can talk, dipsquid, what do you think I am, an idiot?" the creature huffed and crossed his arms in front of his naked chest. "My name is Noctis by the way, what's yours?"

Prompto opened his mouth and closed it a few times until he actually found his voice again.

"I... I'm Prompto? I-I mean, um, yeah. My name is Prompto."

'Great. Impress the potentially dangerous siren with your great ability to say your name,' Prompto thought and groaned inwardly.

"Prompto? That's cute," the siren smiled nevertheless and exposed his teeth, that were layered deep into his mouth. Kissing that must be quite a hassle, Prompto had thought then, just to startle at his own mind's discourse.

"I-is it? Everyone thinks it's pretty weird and old-fashioned. Sometimes I think it'd've been easier if my parents had come up with 'Peter' or something," Prompto rambled, just to blink as he realized that he was telling a stranger about one of his biggest secrets. "Um... Sorry. I didn't mean to... To bother you with that kind of stupid stuff..."

"Well, if you'd rather be called Peter, I can call you that, but I kind of like Prompto. It suits you," Noctis shrugged, his tail splashing where he was still halfway in the water.

"I-it does?" Prompto stammered, feeling his cheeks heat up in embarrassment. "Wait, are saying this because you think I'm cute??"

"Naturally," the siren grinned, exposing more of his teeth.

Prompto was both fascinated and scared by those, but he continued to ask the siren about anything and everything until it had gotten cold and he needed to go home and catch some sleep. But not without the promise to return the following day.

That had been over a month ago. Since then, Prompto and Noctis had become friends, went swimming together and explored the places near the shore, both above and under the water surface. Prompto told Noctis about the world of the humans and in return, Noctis told him all about his home, the ocean and the community of the sirens.

Sirens weren't all that different from humans, just that they lived in a very hierarchic system with a king and everyone else served under. As it turned out, Noctis was the prince and thus the second in line. For a while it boggled Prompto's mind that a simply boy like him was friends with the prince of a whole different species, one so much more advanced than his own.

Or at least that was how the sirens seemed to him.

Due to their hierarchical system, higher-ups were entitled to judge and prosecute all kinds of crimes. If there were any problems, the one higher up had the right to do the same to the self-proclaimed judge and by the end of the day, it was Noctis' father, King Regis, who had the last say in any and all conflicts and he didn't shy away from killing those he found in the wrong. Noctis described his father as kind and loving and while Prompto was scared to meet someone with so much power, he was still curious to see if Noctis' father was just as beautiful as he was. 

Today, he had agreed to meet up with Noctis to talk about a new game that he had bought, something that Noctis had become quickly interested once Prompto had shown him a few games on his new, waterproof phone three weeks ago. They had taken pictures together and more than once Noctis had been staring at the selfies Prompto had taken at home to mark his weight loss. He was proud of that, but somehow Noctis found it interesting to stare at those half-naked pictures of him, when he would sit just as half-naked next to him on the beach.

When Prompto had asked him why, the siren had simply replied with, "Your pants are different."

Well, of course they were. Prompto preferred loose fitting bermuda shorts when he went swimming and tight-fitting boxer briefs under his school uniform. Since it was his last year and his pants were slowly getting a little too small to hide any accidental boners in it, he wore tighter underwear so that it wouldn't stand out too much if the accident came around.

Prompto secretly blamed Noctis for being a pervert, who just wanted to see him naked, but then again, given the nature of the other, he probably wasn't used to people being clothed. He would time and time again look at his legs and poke his ass and ask if the stitched on seam at the front was the opening for his penis and hole and while that had led to an awkward tale about the mating of humans, Prompto had never learned how sirens had sex in return.

Not that he wanted to ask, but it wasn't like he wasn't interested. Especially since Noctis had asked him so many questions about details and such. For Prompto, who only had had a relationship with his hand so far, this had been so much to talk about that he had been fully exhausted and had to retire for the night. Needless to say that Noctis looked disappointed and hadn't brought up the topic since.

Prompto arrived at the spot under he wooden pier where they always met and looked around for Noctis. Usually, the siren would be there before him,taking a nap on the stones at the far end, where the water was deep enough for the fishing boats. This time, however, Noctis was nowhere in sight.

Even though Prompto didn't think it was out of the ordinary, he was a little worried. Usually, Noctis would say something if he thought that he would be late, so why not this time? Still, Prompto set up his towel and started his portable console to play a few rounds on his own, looking up every now and then to figure out where that strong smell of sweet prawns and seaweed came from. He suspected that someone was having a barbecue a little further down the beach as was usual at this time time of the year, but he couldn't make out the telltale smell of coals burning.

An hour after their promised meeting time, Prompto decided to go looking for Noctis. He left his things in a heap behind a pillar, hidden away from prying eyes, before he stepped into the water, calling out for Noctis. The further he waded into the water, the smell of prawns and seaweed intensified and on a whim he decided that if he couldn't find Noctis, he could at least find out where _that_ came from. Who set up a barbecue at the end of the pier?

The closer he got to Noctis' usual resting point, the more the smell intensified and somehow that didn't match up with his theory about a barbecue. Frowning, he moved closer to the stones and stepped around them, startling into a halt when he caught glimpse of a large black fish tail.

"Noct?" He asked tentatively, moving around to see if he was right about his assumption.

"Don't come any closer!" 

Prompto startled, but stayed where he was. This wasn't Noctis' usual voice, this one was deeper and less human. The cry he had just heard sounded more like a shriek of an animal than the almost human friend he had made in the siren.

"Why?"

For some reason Prompto was really surprised how calm he sounded in the face of possibly getting maimed and eaten alive. A long pause of silence followed during which Prompto dared to move around the stones until he could see Noctis in all his glory.

He looked like he was sick, his tail curling and unfurling, slapping angrily against the surface. His eyes weren't blue anymore, but burning red into Prompto with a primal hunger that the blond couldn't quite place yet. He just knew that it sparked something inside of him that drew him closer to the siren. He only hesitated because Noctis was baring his many lines of teeth at him in a hiss.

"Noctis... what... What is going on?" Prompto asked, staying out of touching range for the siren, although he was pretty sure that if Noctis suddenly charged at him, he would be rooted on the spot, unable to save himself. Seriously, thinking about it, Prompto wouldn't stand a chance against Noctis in any case.

"Stay where you are!" Noctis hissed, baring his sharp teeth while his chest heaved heavily. 

"I get it, I get it!" Prompto gave back with an exasperated sigh. "I won't move any closer, but _please_ tell me what's going on."

Still panting as if he was fighting a heavy fever, Noctis watched him like a hawk for a few moments until he seemed to have calmed down a bit. He took a deep breath, the gills at his neck fluttering nervously.

"You... you never asked... how sirens... _mate_ ," Noctis started and it didn't take much for Prompto to put two and two together.

"...you're in _heat_?! Like... like a _cat_?" He gasped and stepped closer, just to be hissed at by the siren. 

It was so ironic that he almost started laughing. It was only the miserable look on the siren's face that let him keep his face straight. "Sorry."

Noctis hissed once again, but huffed and looked away, obviously trying to calm himself once again.

"It's... For us sirens, it only works when... we've... _bonded_. I... didn't expect it... to happen..." he trailed off, and suddenly the smell of sweet prawns and seaweed intensified once more, leaving Prompto a little dizzy. Nevertheless, the smell drew him in and he took a step forward.

"Don't!" Noctis hissed, splashing his tail and flaring his gills.

Prompto blinked and stopped moving. "Noctis... Are you telling me... You've _bonded_ me?"

Noctis hissed again, sinking deeper into the water so that the sound turned bubbles.

"...Really?" Prompto asked, feeling all bubbly inside as his heart made a leap and started to beat faster and harder before. "I... That's... Thank you!"

"What the fuck... Why are you _thanking_ me?" Noctis growled, getting back out of the water.

"Because! That's... I've never been confessed to before and it's the best thing that's ever happened to me," Prompto giggled, tilting his head to the side with a big smile.

Noctis stared at him dumbfounded for a moment before he growled and disappeared under the surface and came back up right in front of Prompto. The smell of prawns and seaweed was almost unbearable then, but to the blond, it was still alluring and he felt himself drawn to it. The siren's eyes were still glowing red, hypnotizing Prompto even though he tried his best not to be affected by it.

"...A siren's heat usually lasts a day... longer if we can't give in to them. They aren't... exactly painful, but... it's torture. Hell. As if we're left out on the beach to dry. It feels like I'm slowly suffocating and there's _nothing_ I can do about this. I'm _dying_ here... Prompto," Noctis whined, but to Prompto, it sounded more like a purr and the vibrations from his voice went straight to his core. He bit his lip, took a deep breath and then raised his hand to touch the siren's cheek.

"Noctis," he said, watching the other flinch instinctively away from the touch until he realized that there was nothing dangerous going to happen, nor that Prompto was pulling his hand away. Once he realized that, he scooted closer and nuzzled into the touch, making a loud, content purring sound. Snorting softly, the blond let his thumb slide over the little, golden scales on the siren's cheek, feeling some of them come loose and cover his thumb.

"If it's me that you want... Please take whatever you need," he said softly, managing a lopsided smile. He could see those red eyes widen with desire, just before Noctis slipped away from him.

"No... No, you don't want that," Noctis whispered, although Prompto could see his desire and hunger grow in his eyes. "It's enough that I bonded myself to you, it doesn't have to be like this for you as well..."

"Noctis, it's okay," the blonde assured him, leaning back in. "If there's anyone I'd want to do this with... It has to be you. Please, I want... Let's make this a mutual bond, okay?" 

Despite his obvious desire and agony, Noctis hesitated and looked closely at the blond.

"There's... One more thing that you need to know..." He breathed, already having a hard time to keep his desires in check.

"What is it, Noct, please, you can tell me everything," Prompto all but begged, moving forward once again.

"Sirens... Bond for life," Noctis explained, his voice strained with the effort not to attack Prompto. "Once we chose someone... There is no turning back. Prompto, I need you to understand this. I can... I can go back and pretend it didn't happen, I will probably get paired off with another siren anyway for political reasons in a few years. This isn't your fault and you never asked for this. I'm sorry this happened-"

"I'm not," Prompto interrupted quickly. The siren's eyes widened at him, the red glow making him shiver. Prompto scooted closer and touched Noctis' cheek again with a sheepish smile.

"I mean, I'm probably underestimating what this means, but if we both are bonded for life, it means that... You'll always be my friend, right? We'll be together always and forever, right? I know we've only known each other for such a short time, but... I can't imagine my life without you anymore. If this is... How you feel about me, I might just have bonded myself to you as well, although I don't think this is how it works for humans," Prompto chuckled, licking his lips. "Bonding for us is kinda... An optional thing. But I want this with you."

"...are you really sure... I... Don't do this because I'm like this. I... I will manage," Noctis protested, his gills flaring again as he unintentionally bared his teeth again.

Prompto shook his head. "I mean, I'd be lying if I said I wasn't afraid to help you out, but as I said... If this means we'll be friends forever, I'm willing to take the risk."

Noctis narrowed his slitted eyes at him. "You do realize that what I need is far beyond friendship, right?"

Prompto blushed, his eyes dancing around until they landed on Noctis' face again.

"...yeah."

"I might hurt you. In ways you don't want," Noctis warned as he moved closer after all, as if he was stalking his prey. "I will bite you. I'm not sure if I can hold myself back..."

"You... You're not going to eat me up though, right?" Prompto asked, suddenly regretting his brave words.

Noctis shook his head as he came up and let his hand caress Prompto's cheek before it came down to the blond's neck. "No."

"Will... Will I get pregnant?" Prompto asked, his irrational fear of alien eggs growing inside of him, bursting his intestines open, acting up.

Noctis chuckled, a warm sound that lulled Prompto into feeling safe and he had to wonder why he even felt afraid in the first place. "No, I don't think you can. Not from what you've told me about humans."

Somehow, it felt as if that was only half of the answer, but Prompto couldn't work up the nerve to ask about that. Because why should he? Noctis was there and Noctis would keep him safe.

"Okay, good. But, I don't want to drown either, can we, like, go back to the beach?" He asked nevertheless, even as Noctis wrapped his other arm around the blond's waist to pull him in closer.

"I'll take us," Noctis promised, leaning in to sniff at Prompto's neck, making the blond shiver. He opened his mouth and let his teeth graze the freckled skin teasingly.

Exhaling with a shudder, Prompto tilted his head to the side for better access and he could feel Noctis hover over his pulse point, teeth bared, but a second later the siren had pulled him back towards the shore, making good on the promise to continue at the shore.

"Take it off," Noctis hissed and tugged at the hem of Prompto's swim shorts.

"S-sure!" The blond scrambled to say and pushed the garment off his hips. The sand under his back was uncomfortable and he was sure that he would find it in places where he didn't think he could have it later. But the hunger with which Noctis looked at him made up for a lot of things.

"So this is how yours look, you just hide it with clothes all the time instead of a pocket like this," Noctis purred, letting his hand caress Prompto's chest down to his manhood. He was half-hard already for some reason and when Noctis touched him with his cold, slick hand, he wondered exactly what the siren meant.

He didn't have to guess for long though, because even as Noctis was hovering over him, seated between his legs, the siren reached out to take the blond's hand and place it on a spot at the front of his black and golden tail.

"What...?" Prompto started, just to almost jump out of his skin when he felt something _wriggle_ and poke out of a slit he hadn't previously noticed.

He pulled his hand back as if it was burned to look flabbergasted at what he guessed was Noctis' groin, just to see a thin, worm-like _thing_ poke out of it. His eyes widened in surprise and he looked up into Noctis' face, just to see the other nod at him.

"That is mine," he explained and Prompto looked down again, fascinated to see the appendage still wriggling and growing out of the 'pocket'. Soon, it looked nothing like a worm anymore, that was just the tip. As it grew, it turned out to look more like... like a tentacle, growing in thickness to the base. Since Noctis wasn't fully hard yet, Prompto had no idea how long or thick his penis would turn out to be, but it was already safe to say that Noctis' dick was both longer and already thicker at the base than his own dick. Plus, it wriggled and moved around like a tentacle as well, making Prompto wonder how that would feel inside.

He blushed deeply and looked back up, excitement written all over his face. Then he looked away, because he couldn't fathom that he was really so eager to lose his virginity to the siren just because he was in heat.

"It's... _totally_ different from mine," Prompto gushed and reached back out to touch the tip of his index finger to thin part at the end of it, just to pull back in surprise when Noctis gave a sort of pained squeaking sound.

"Sorry! Did I hurt you?" Prompto asked nervously, his hand still hovering over the siren's dick. What if he did? How was he supposed to know what he could do and what not?

"N-no," Noctis ground out between his sharp teeth. "It was good... _Hurry_... I don't know how long I can... control myself..."

"O-okay," Prompto replied meekly and pulled his hand back. "What... Do you want me to do?"

"Just... hold still for a moment," Noctis hissed and slid his hand further over Prompto's front, below his dick and fondled his balls. Moaning, Prompto's threw his head back, feeling goosebumps all over his skin. 

"Where... _where_ is it?" Noctis growled, even as Prompto got lost in pleasure.

"H-huh?" The blond gasped, trying to get his wits together enough to ask Noctis what he was trying to achieve. "Where is _what_?"

"Your... your _hole_!" Noctis growled. "Where is your stupid hole so I can _fuck_ you?!"

Prompto blinked, then hissed because one of Noctis' long nails scratched over his scrotum in his rage. "It's... Well, I guess _yours_ is... _there_ , just below your... your _dick_. Mine... um, I dunno what you usually do with it, but, um, I guess you mean my asshole and I usually shit through that-"

"Don't we all?" Noctis glowered, looking impatient at where Prompto wanted to go with his speech. 

The blond stared up at the other for a moment and then huffed indignantly. "I guess? I mean, um, I dunno how that works for _you_ guys, but my virgin ass has never been... _fucked_ , so it's gonna be pretty tight and, and... Um... I-I know you said it's gonna hurt but..."

"Where. Is. Your. _Hole_?!" Noctis growled, baring his rows of teeth and Prompto squeaked in fear.

"Behind! On my... my back!" Prompto cried, eventually making Noctis back up.

"On your back?" The siren asked and Prompto nodded vigorously. "Well then, turn around!"

"O-okay," Prompto agreed and shifted to rotate underneath the other's body. Which turned out to be rather complicated since he had to coordinate his legs and not kick Noctis accidentally anywhere. Besides, he'd rather not have sand on his dick, so he grabbed his discarded swim shorts and put them under his crotch before he lowered himself on the ground. It didn't help _much_ , but it was at least better than nothing.

"C-can you see it?" Prompto asked as he had turned around and looked back over his shoulder.

"I can," Noctis husked and put his hand on Prompto's ass cheeks to pry them apart. "Such a small, tight-looking hole..."

The hunger in the siren's voice sent goosebumps up and down his spine, making him moan despite his sudden bout of new fear. Instinctively, he lifted his ass up for better access and heard a splash coming from a tail slapping impatiently in the water behind them.

"My Prompto," Noctis growled and shifted until his front was pressed to the human's back. As his mouth latched back on Prompto's neck and shoulder, gracing teeth over the blond's skin, his dick wiggled its way up in the cleft, finding the puckered entrance. There, it started making its way inside by wriggling forward and past the tight ring of muscle.

It felt weird, but Noctis successfully distracted him by scraping his teeth over the juncture of his neck. Also, his dick was smooth and slick, lubricated from the tip as precum kept dribbling out and from the base, where his opening kept providing lubricant so that it wouldn't dry out in the water, or so Prompto reasoned.

As the girth increased with the length of the cone-shaped appendage, Prompto found himself opened up wider and wider, Noctis forcing his way inside until Prompto felt like he was being split apart at the seams. Still, even though the stretch should be unbearable for his virgin ass, a warm, powerful feeling much like happiness was pooling in his core that spread throughout his whole body even as he muffled his cries in the crook of his arms.

After a while, Prompto thought that surely, Noctis must be all the way inside of him already, but he kept going on and on. Unable to cope with the situation and the anticipation anymore and since crying out wasn't enough anymore, Prompto kicked his leg into the sand on either side of Noctis' tail, which obviously tickled the siren because he growled and started kicking faster himself.

"Fuck, Noct! It's so big, go slower!" he gasped, just to cry out when he felt sharp teeth sinking slowly into the skin of his shoulder. "Ow, _fuck, fuck, fuck_!"

Before he knew what was happening, Noct started thrusting. Prompto was confused because he didn't know when the siren had deemed him to be ready, but obviously Noctis was past his limit and just moved on instinct.

It stung, but the warm feeling was still there and Prompto couldn't help but feel proud that he was able to help the siren. Even if his body hurt, the pleasure and feeling of accomplishment were more than enough to make him happy with the situation.

The friction and added lubrication was slowly helping to make him relax and if it weren't for the pain from his shoulder, Prompto might have been able to fully relax. His body was slowly getting accustomed to the thrusts and soon, Noctis snaked a hand around his waist, bumped into his erection and then obviously decided just to go with it. He wrapped his scaly hand around it and squeezed the base, making Prompto see stars for a moment and he couldn't help but moan at the stimulation.

Inside of him, he could feel Noctis' dick wriggle around, brush against different spots which Prompto found weird until it brushed against a spot that made him gasp. And then moan as it did it again. Soon, he was moaning with every brush of the thin tip against that spot and he pushed back actively as well, feeling his orgasm approaching.

"Prompto... I'm close," Noctis growled, which was his only warning before the siren doubled his efforts and thrust a lot harder and faster, making Prompto cry out despite himself. It was only when he was lifted off the ground by strong hands on his hips that Prompto realized that he wasn't the only one making a sound, but he couldn't quite think clearly as his head was swimming from his own approaching orgasm. While a shrill whistle filled the air, followed by a loud trill and clicking sounds, hot cum filled Prompto up inside, spilled into him until he felt like his stomach was going to burst and with all that pressure he came, gasping as his own cum splattered down into the wet sand and his swim shorts.

He gasped for breath as he tried to get a grasp on reality again. His mind was still reeling as he replayed the moment in his head and then remembered the weird sounds that Noctis had made as he came.

“Holy shit, dude. Did you just make that sound?” He asked, still panting as he turned his head around to look at his lover.

"That's... that's what I wanted to ask," Noctis huffed, looking all flushed dark and dry and _sweaty_. His tail swished nervously and he sprayed water over them in the process. "You sounded like a dying walrus or something."

"Y-yeah? Well, you sounded like... like... I don't have anything, but it sounded _so weird_!" Prompto sputtered, wiggling his legs so that he could turn around and face the siren. "That didn't sound like... like _anything_ someone should be able to make!"

"You mean it sounded _inhuman_ ," Noctis deadpanned before he humored Prompto and slithered back into the water, pulling out of him at the same time.

If Prompto had thought that Noctis felt long when he pushed in, _now_ he felt like there was going to be no end at all. He held his breath for the first few centimeters, completely forgetting the retort on the tip of his tongue, but as he realized that this would only make him tense up, he breathed as evenly as he could until Noctis was all the way out.

His ass still felt as if it had been split in two and it was pulsing with pain, but there was also the feeling of being full with Noctis' cum. He pushed himself up on his fours and groaned when he felt a big part of the cum inside of him flow out. After the first wave was over, he actively tried to push the rest out, amazed at just how much the siren could cum.

Turning around to start cleaning himself off in the ocean, he caught Noctis staring at him with wide eyes and flared gills, breathing heavily.

"Fuck," was the only thing Prompto heard the siren whisper, before he was tackled back to the ground, very eagerly and without a chance to fight back. He could feel the siren's tentacle-like dick probing at his opening again, and he opened his mouth to protest, but Noctis just pressed their lips together hungrily.

As he kissed him senseless, Prompto melted against the other and spread his legs, letting his dick wiggle back inside as if it was its home. Sure, the sand on his back hurt a bit, but it was nothing against the pleasure that he felt from being desired by such a special being like Noctis.

Soon, the siren was back all the way inside of him, with the only difference that they were hugging now. Prompto wrapped his legs around Noctis' middle and hooked his feet together, just to moan and gasp every time the other's dick would move against his prostate again, doing everything desperately to make him feel good. Prompto tried to return the sentiment by squeezing and milking the other's dick, which Noctis rewarded in return with more kisses and nips and outlandish sounds that were obviously expressions of his satisfaction level.

Quickly, Prompto found himself getting closer to his second orgasm, and he started to suspect there was some kind of aphrodisiac in the siren's body fluids that made it easier for him to relax. Something about hormones and pheromones to make the receiving party pliant to your advances. Some animals did that, right? Then again, Prompto was never good with biology.

As the siren's tail splashed in and out of the water with every thrust, Prompto clung to him for his dear life, looking forward to feeling the other cum again. After a few moments, he had to close his eyes because seeing Noctis' lustful face was almost too much for him. Prompto only opened them again when Noctis started to make that sequence of whistles, trills and clicking sounds. Prompto watched in fascination as the different stages of satisfaction washed over the siren's face, making his gills flutter. He bared his fangs and the rational part of Prompto's brain thought that he should be scared by how ferocious the siren looked liked this. Then again, Prompto's rational part knew that the fear was futile because he would stand literally no chance against the other should he decided to eat him up. Or just, well, simply kill him. Like a mantis after sex.

But wait, with mantisses it was the female that killed the male, not the male, right?

Prompto's train of thought was cut short when the trilling sound continued and intensified. Surprised, he held his breath and looked up to look at the siren's face as he came this time around, filling him up once more. Moaning, Prompto stroked Noctis' back through it, trying to encourage him to keep going, to let it all out because the intensity seemed to have only grown. It didn't take as long this time, but long enough for Prompto to commit Noctis' ecstatic face to his memory. He was so distracted by it that he didn't really cum himself.

When he was done, the siren collapsed on top of him, but that didn't stop Prompto from stroking his back soothingly. He relished in the feeling of scales underneath his fingers, how cool Noctis' leathery skin was to the touch, even as his own erection was still pulsing hot between the two of them.

When Noctis had collected his wits enough to be able to think clearly again, he pushed himself up and blinked down at Prompto, who noticed an extra pair of lids closed and opened with every blink.

"You didn't... this time," Noctis noted breathlessly, blinking down at Prompto again.

"No," Prompto chuckled sheepishly. "Guess I was too focused on you. You looked... so good when you came."

The siren blinked again, his eyebrows twitching into a small frown. He let out a few unhappy trills and Prompto couldn't help but giggle. "Those sounds you make... they're cute."

Noctis' frown turned into a confused glare. "Are you making fun of me?"

"No, I think it's cute... Is this how you sound when you're not speaking... with humans?" Prompto asked, getting suddenly aware that Noctis' dick was still inside of him.

"...When we communicate over long distances. The water transports these sounds better than human words," Noctis explained and frowned still. "But what about you?"

"I'm not the one in heat here, it's not a life-or-death situation for me if I don't cum," Prompto replied sheepishly. "But... I'm close, so if you're ready to go again, I'm sure I can think of something..."

"I can go again, but not so quickly," Noctis admitted, maybe a little sheepish.

"Hm? But you're not opposed to getting touched there?" Prompto asked and squeezed the appendage inside of him.

Noctis gasp was enough of an answer for him. He grinned and pushed at the siren's side so that he would roll over and get off him. "I'll show you something, not sure if it's as good for you as it is for humans... but I'm sure it is," Prompto said to soothe the glare of abandonment that started on Noctis' face.

"...Okay," the siren said and finally turned to lie on his back. His tail was the only thing left in the water, but for what Prompto had in mind, he didn't need to be that far out of his element.

"You can slip a little further into the water," Prompto said, scooting backwards a bit himself. "It must be uncomfortable to dry out, right?"

"It's okay," Noctis said, still eyeing the blond curiously, who then moved to straddle that powerful fishtail.

"Okay schmokay," Prompto giggled as he got into position. He looked at the siren's dick, which was lighter colored than the rest of Noctis' body, more of a grey than black like the rest of him. It was still oozing cum and Prompto used first his spit and then the ocean water to clean it a little. It was smooth, much smoother to the touch than Noctis' back, not as leathery but soft, just like Prompto's own skin. He smiled as he felt it twitch under his ministrations, glancing up to see Noctis bit his lip as he watched his hands curiously.

Once he was satisfied with his cleaning, Prompto leaned forward and licked a stripe up the wiggling appendage. Noctis let out a series of new trills and clicks that made Prompto chuckle and he tried to lick him again, just to get slapped in the face by the siren's dick.

"Hey!" he protested, using both hands to keep it still , which elicited even more clicks and trills from the siren and a heated glare of protest. "Don't give me that look, I know you're secretly enjoying this," Prompto chided before he leaned in again and took the tip of Noctis' dick into his mouth.

It tastes salty, but well, that was to be expected after washing it with ocean water. The taste that came afterwards was... tangy, not too good, but Prompto could manage. What was infinitely better than the taste was Noctis' reaction.

The siren made a sound that Prompto could only identify as some kind of squeak, followed by some whistles that sounded suspiciously like a groan. Those sounds grew in volume when Prompto swirled his tongue around the narrow end and the flesh in his hands seemed to grow as well, pushing deeper into his mouth.

He pulled away and grinned. "Good, huh?"

"...yeah, what the fuck is this?" Noctis gasped, already panting from what Prompto was doing to him.

"It's called a blow job," Prompto explained and licked his lips. 

"I like it. More?" Noctis asked, blinking cutely in a way that made Prompto laugh. 

"Sure, but warn me before you're cumming," Prompto hummed and took the siren's dick back into his mouth. Somehow it was easier with this shape than the dildos Prompto had had his first experiences with. It was much thinner at the tip than a human dick, so it was easier to wrap his lips around. He didn't want to try deep-throating it though...

"Prom... I'm close," Noctis warned just when Prompto was about to try anyway. Pulling off with a plopping sound and a gasp, Prompto straightened again and stretched his back again.

"Okay... Let's see if this will work," he hummed and scooted forward so that he was straddling Noctis' tail just where his dick poked out of its pouch. He guided the wiggling thing to his entrance, that was still well lubed from their previous round. Not that it needed to be, but it definitely made it easier to slide the thing back in again.

As Noctis let out his excited trills and whistles again, Prompto sank lower and lower, feeling the dick go deeper and deeper inside of him until he was sure that it was poking his stomach from the bottom. Contrary to his expectation, it didn't hurt though. Quite the opposite, being able to take such a big and long dick was somehow elevating, _satisfying_. Even if that meant that his ass was stretched wider than he had ever thought humanly possible.

"Fuck... Noct, you're so _deep_ ," he groaned, grinding his hips down to earn another series of clicks and whistles.

"What... what are you doing," Noctis said, not sounding like he wanted a verbal answer, so Prompto just started moving. He rode Noctis slowly at first, as if he was testing the waters, but whatever pheromones the siren was emanating, it made him move faster and harder, grinding down as if nothing was good enough.

And it felt _good_. It hit every spot that felt good and soon he was seeing stars, closing his eyes to forget where he was as he concentrated solely on the pleasure. Noctis' trills and clicks and whistles where his background soundtrack and it was _good_. His dick kept wriggling inside of him and it didn't take him long to find his completion. This time he came even before Noctis, but it didn't take the siren long to follow him over the edge.

Minutes later they were still panting and gasping, until Noctis scooped him up into his arms and pulled him into the ocean, underwater, just to smother him with a kiss. Prompto protested, panic setting in that he would drown any minute now, but as something passed from Noctis' mouth to his, he didn't feel so weird inhaling water anymore.

' _What...?_ ' he asked, blinking in surprise when he realized that he could even speak underwater.

' _I'm sorry I went ahead... but I don't think I could bear to live without you anymore,_ ' Noctis admitted, looking sheepish where he floated just in front of Prompto.

The blond touched his neck, feeling three lines of gills on either side that fluttered with every breath that he took. He looked up in surprise. ' _Is this...?_ '

Noctis nodded.' _With these you can breathe underwater just like us,_ ' he explained.

A new bout of panic rose inside of Prompto and it must have shown on his face because raised his hands quickly.

' _You'll be able to breathe in land just fine,_ ' he added quickly. ' _Really, this is just an addition. So that you... You can be by my side if you want to be..._ '

Prompto blinked, unable to believe his ears. He touched his gills gingerly again, wondering how they would look like on land. It was only then that the meaning of Noctis' words sunk in.

' _Wait, is this a proposal?!_ '

Noctis bashful nod was confirmation enough.

' _Dude, there must be, like, countless mermaids or sirens or whatever that would be much better suited to be your partner than I! I mean, I can't even bear your children or anything!_ ' Prompto protested, although he felt very flattered by the proposal.

' _It's okay if you don't want to,_ ' Noctis said, but looked entirely crestfallen to be pushed away so quickly. ' _But I'm bound to you anyway, it wouldn't make sense find someone else._ '

Prompto blinked, thinking back to the beginning of their meeting today. ' _Bound for life, huh?_ '

' _Yeah,_ ' Noctis confirmed with a simple nod and another bashful smile.

Prompto thought about it. He liked Noctis, too, and he was sure that after today, he would never be able to have 'normal' sex. And Noctis was, like, a prince, so that would make him a princess, right?

He heaved a breath and then said, ' _Well, if having kids isn't too much of an issue for you..._ '

' _No. I just want to be together with you forever and always,_ ' Noctis admitted, swimming a little closer so that he could take Prompto's hand and put it in the middle of his chest. It felt weird, but only until Prompto realized that Noctis' heart was beating in unison with his. ' _It has to be you. I love you._ '

' _Holy shit,_ ' Prompto gasped, unable to fathom his luck. ' _Okay, me too, I accept your proposal. I... I think I love you, too. I mean, I've never felt anything like what I feel for you, and it's pretty intense, so yes, I guess it's love._ '

Seeing the siren's face light up with happiness was enough for Prompto to confirm that what he was feeling was love indeed.

' _You're the best,_ ' Noctis thrilled and wrapped himself around Prompto to pull him deeper into the ocean. He placed kisses all over him, intermixed with little bites and nips, even as Prompto worried about getting crushed about the masses of water.

' _Besides... when it comes to bearing children... That's something I can do,_ ' Noctis admitted with a blush that left Prompto gaping. He looked away bashfully and then said, ' _I need to introduce you to my father, he's_ so _excited to meet you. ...Prompto?_ ' 

But poor Prompto had fainted.

**Author's Note:**

> I swear this wasn't just about mer-dicks... I kept running out of synonyms though. XD


End file.
